Special Telemeters and Custom Nomographs

Tutorials and setup instructions for specialist or custom-made Telemeters.

Wndsn Universal Moon Clock

A visual aid in determining Moon phase, the Wndsn Universal Moon Clock[1] is a simple equatorium predicting cardinal direction, and approximate average time (in unequal hours) from observed lunar shape and altitude; using the front side for the northern hemisphere and the mirrored reverse side for the southern hemisphere.

This is a teaching tool showing ideal (equinox) conditions; the directions and times throughout the rest of the year have to be extrapolated.

Wndsn: Universal Moon Clock How To

Example: Waxing gibbous. Observation at 6 PM (Sunset at equinox). Moon rises (east), according to the arc at 3 PM and now, (3 hours later) is at south-east. Zenit (south) is reached at 9 PM and the Moon sets at 3 AM (west).

Approximating Time of Night

[All times are given in unequal hours.] For the Sun, we know that sunrise is at 6 AM, noon is at 12 PM, and sunset is at 6 PM. Halfway (+3 hours) between rising in the east and its zenith, the Sun marks 9 AM. At noon, the Sun is at its zenith, and at 180° azimuth, due south (as seen from the northern hemisphere). Halfway (+3 hours) on its way from zenith to sunset, the Sun marks 3 PM.

That same holds true for the full Moon. Thus, for the full Moon, at its zenith, this means that it is midnight.


The symbols and scales depict the Moon as viewed from the northern hemisphere. For observations from the southern hemisphere, the directions and positions are mirrored and the Moon clock works by turning it over and looking at the scales from the reverse side.

Due South

A line through the points of the waxing or waning Moon indicates due south and, the further south we go in the northern hemisphere, the more tilted the shape of the Moon appears.

General Notes

The underlying times are based on unequal hours (day = 1/12 + night = 1/12) (and sunrise at 6 AM) and are valid as is on the equator and on the equinoxes. For all other times and locations, the unequal hours are to be understood as average times and have to be converted to, or estimated in 1/24 (equal) hours.


  1. Wndsn Universal Moon Clock 

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